When it comes to the mining sector, U.S. Pat. No. 7,896,580 B, for example, discloses an anchor with expansion heads. The expansion heads are installed, especially screwed, like a sleeve onto the anchor rod (typically a solid rod, rarely a hollow rod) at the end facing the ground and they expand inside the substrate when screwed or pulled after the anchor has been put in place.
The diameter of the drilled hole needed for the installation of the expansion-head anchor, however, is often relatively large, e.g. 32 mm to 34 mm for a 16-mm anchor rod, which can especially be due to a relatively complex structure of the expansion head which takes up a lot of space. In certain cases, this can also give rise to problems when the relatively large heads are inserted into the drilled hole, particularly when the drilled hole is unstable or not completely straight. Moreover, the force introduction of an expansion head, owing to its fundamental shape as well as to tolerance fluctuations, is often very punctiform, so that in certain cases, especially with a weak geological formation, the compressive stress that the surrounding rock can withstand might be exceeded. Furthermore, before the anchor has been installed, expansion heads are sometimes not very sturdy since they consist of several parts that are often only held together loosely. Only after the expansion effect has been activated are the individual components held together positively as well as non-positively. This means that, under certain conditions, the expansion sleeves can be damaged when the anchor is transported underground.
German patent applications DE 20 63 843 A and DE 10 2010 002 214 A also disclose screws that are made of solid material and that are anchored punctiformly at the end of the drilled hole.
German patent application DE 10 2007 000 829 A discloses an anchor tube whose interior contains a curable compound. The curable compound is dispensed into the drilled hole, thus securing the anchor tube in the drilled hole.
German utility model DE 297 07 502 U1 discloses a screw-injection anchor whose lower end has an anchor tube fitted with a fixing nut which can be screwed into the ground, whereby a hydraulic mortar can be injected through the anchor tube into the surrounding ground via openings in the tube wall.